/*
 * 函数防抖 immediate true 表立即执行，false 表非立即执行
 * */
export function debounce(func, wait, immediate) {
    let timeout;
    return function () {
        let context = this;
        let args = arguments;
        if (timeout) clearTimeout(timeout);
        if (immediate) {
            var callNow = !timeout;
            timeout = setTimeout(() => {
                timeout = null;
            }, wait);
            if (callNow) func.apply(context, args);
        } else {
            timeout = setTimeout(function () {
                func.apply(context, args);
            }, wait);
        }
    };
}
export function debounce2(func, wait, immediate) {
    let timeout, args, context, timestamp, result

    const later = function () {
        // 据上一次触发时间间隔
        const last = +new Date() - timestamp

        // 上次被包装函数被调用时间间隔 last 小于设定时间间隔 wait
        if (last < wait && last > 0) {
            timeout = setTimeout(later, wait - last)
        } else {
            timeout = null
            // 如果设定为immediate===true，因为开始边界已经调用过了此处无需调用
            if (!immediate) {
                result = func.apply(context, args)
                if (!timeout) context = args = null
            }
        }
    }

    return function (...args) {
        context = this
        timestamp = +new Date()
        const callNow = immediate && !timeout
        // 如果延时不存在，重新设定延时
        if (!timeout) timeout = setTimeout(later, wait)
        if (callNow) {
            result = func.apply(context, args)
            context = args = null
        }

        return result
    }
}
